Process for production of rotary anodes for roentgen tubes

ABSTRACT

A process is described for imparting resistance to rotary anodes for X-ray tubes by spraying a graphite base with tungsten or a tungsten alloy, followed by depositing an outer coating of tungsten or an alloy thereof from the gaseous phase.

United States Patent 1151 3,649,355

Hennig 5] Mar. 14, 1972 [54] PROCESS FOR PRODUT1ON 01F [58] Field of Search 1.1 17/93.1, 228, 217, 227; ROTARY ANODES FOR ROENTGEN 3135013111330 TUBES [56] References Cited [72] Inventor: Walter Hennig, Reutte, Austria UNITED STATES PATENTS [73] Assgnef 3:333:52 Bevehpmem Cmmmn 3,085,317 4/1963 Stackhouse ..117/93.1 x 3,157,531 11/1964 Norman et al. ..117/228 X [22] Filed: Aug. 12, 1969 Primary Examiner-William L, Jarvis [21] Appl' 849444 Attorney-Morgan, Finnegan, Durham & Pine [30] Foreign Application Priority Data [57] ABSTRACT A process is described for imparting resistance to rotary Ausma "7861/68 anodes for X-ray tubes by spraying a graphite base with lungsten or a tungsten alloy, followed by depositing an outer coat- [52] 11.5. C1 ..ll7/2l7, 117/227, 117/228, ing oftungsten or an alloy thereoffmm the gaswus pham ll7/93.1PF,l17/107.2 R, 313/311, 313/330 [51] Int. Cl. ..H01j 1/05, HOlj 35/08 12 Claims, 1 Drawing Figure PROCESS T0112 PRODUCTION OF ROTARY ANODES FOR ROENTGEN TUBES This invention relates to X-ray or Roentgen tubes and more particularly, to a process for imparting resistance to rotary anodes for X-ray tubes.

in the past, rotary anodes for X-ray tubes have been disclosed which generally consist of a base member made of graphite to which a layer of tungsten, molybdenum, thorium or tantalum metal has been applied. Rotary anodes of the kind described above are highly desirable because of their extraordinarily high load capacity derived, to a great extent, from the graphite base member. Regarding these latter anode types, it has been discovered that when the layer on to which the electrons are emitted consists of tungsten or a tungsten alloy, a brittle interlayer of tungsten carbide forms between the tungsten or tungsten alloy layer and the graphite substrate. The aforesaid brittle interlayer is a distinct disadvantage since it jeopardizes the connection between the covering layer and the graphite substrate.

One way to eliminate this drawback is to place an interlayer of rhenium between the tungsten or tungsten alloy layer and the graphite substrate. However, due to the added costs involved in producing anodes of this type, it would be highly advantageous and desirable to discover a method of eliminating the disadvantage of brittle inter-layer formation while simultaneously avoiding increasing costs. This is specifically what the present invention accomplishes.

Accordingly, this invention discloses and claims a process for imparting resistance to rotary anodes for X-ray tubes which comprises the steps of:

a. spraying a graphite base at the site of electron impact with a metal selected from the group consisting of tungsten and tungsten alloys in order to form a uniform coating thereon; and

b. subsequently depositing on said coating an outer covering layer comprising a metal selected from the group consisting of tungsten and tungsten alloys wherein said deposition is from a gaseous phase.

The first step, i.e., spraying step, comprises the formation of a uniform coating on the graphite substrate at the site where electron impact will take place. Although any well-known spraying method is appropriate, it is preferred to use a plasma gun in the spray application of the uniform coating layer. In this manner, the individual tungsten particles which are heated to high temperatures upon striking the graphite substrate, are cooled very rapidly so that there is little chance of reaction with the substrate to form a brittle tungsten carbide phase. This uniform coating layer applied by a spray technique can consist of substantially pure tungsten or it can be an alloy of tungsten with from about 1.0 to 35 percent by weight of rhenium, osmium, iridium or other metals having high melting points or mixtures thereof as an alloying ingredient.

Despite the effectiveness of the above described spraying process whereby little or no reaction takes place between graphite substrate and tungsten to form the undesirable brittle tungsten carbide phase, the resulting surface is not suitable as a coating layer for a tungsten rotary anode. This is due to the high porosity of such a surface layer.

Consequently, further treatment is required and comprises the second and final step of the instant process.

This second step is a deposition step wherein an outer covering layer is deposited on the uniform coating applied by the spraying technique. This outer covering layer can be substantially pure tungsten or an alloy of tungsten with from about 1.0 to 35 percent by weight of rhenium, osmium, iridium or other metals having high melting points, or mixtures thereof as alloying ingredient.

The depositing of tungsten or a tungsten alloy is accomplished from a gaseous phase which contains the aforesaid tungsten or tungsten alloy. Deposition from the gaseous state is effected in one of two ways: direct vapor deposition under vacuum or precipitation of gaseous compounds. The direct vapor deposition method is carried out under low pressures whereby the gaseous tungsten or tungsten alloy sublimates forming an outer covering layer on the sprayer coating layer.

The second or precipitation method is another highly desirable means of forming an outer covering layer. It consists of precipitating tungsten or a tungsten alloy from the gaseous state present therein as a compound salt, such as tungsten hexafluoride or tungsten hexachloride or mixtures thereof, in a hydrogen atmosphere. Generally, high temperatures, for example 550 C., accompany the precipitation step. Of course, in a similar manner, tungsten alloys can be deposited by utilizing the appropriate metal salts. For instance, if a tungstenrhenium alloy is to comprise the outer covering layer, one may use a gaseous phase consisting of tungsten hexafluoride and rhenium hexafluoride in predetermined amounts admixed with hydrogen gas. At high temperatures, thermal decomposition takes place and a tungsten-rhenium alloy precipitates.

The body or substrate of the rotating anode is made of graphite in whatever shape and dimensions are necessary for the particular application. The tungsten or tungsten alloy intermediate coating layer need not be very thick. A thickness of about 1 millimeter is preferred; however, a range of thickness of from 0.1 mm. to about 5.0 mm is applicable. The outer layer is even less thick and is preferably about 0.2 mm, however, a suitable range is from 0.02 mm. to about 2.0 mm.

In another embodiment of this invention, there is claimed the product which derives from the instant process.

This product is illustrated by the accompanying drawing which shows a cross section of a rotating anode having a disc shaped body 1 made of graphite on which a sprayed tungsten coating layer 2 is superimposed with an outer covering layer 3 of tungsten. Layer 2 consists of substantially pure tungsten and is about 1 mm. thick. It was applied by means of a plasma gun. Over this layer, there is another layer 3 comprised of tungsten having a thickness of about 0.2 mm. It was applied by precipitating a gaseous mixture of hydrogen and tungsten hexafluoride in proportions of 10:1 at a temperature of about 550 C.

In like fashion, the outer covering layer can be a tungstenrhenium alloy which is deposited from a gaseous mixture of rhenium hexafluoride, tungsten hexafluoride and hydrogen.

In any case, the outer covering layer 3 consisting of columnar crystals, is practically non-porous and is highly resistant to impinging electrons.

What is claimed is:

l. A process for imparting resistance to rotary anodes for X- ray tubes which comprises the steps of:

a. spraying a graphite base at the site of electron impact with a metal selected from the group consisting of tungsten and tungsten alloys in order to form a uniform coating thereon; and

b. subsequently depositing on said coating an outer covering layer comprising a metal selected from the group consisting of tungsten and tungsten alloys wherein said deposition is from a gaseous phase.

2. The process of claim 11 wherein said spraying step is accomplished by means of a plasma gun.

3. The process of claim 1 wherein said deposition comprises vapor depositing said metal under vacuum.

4. The process of claim 1 wherein said deposition comprises precipitating said metal from the gaseous phase.

5. The process of claim 4 wherein said precipitation is effected by thermal decomposition of metal salt in the presence of hydrogen gas.

6. The process of claim 1 wherein the tungsten alloy utilized in the spraying and depositing steps is selected from the group consisting of tungsten-rhenium, tungsten-osmium and tungsten-iridium alloys,

7. The process of claim 6 wherein said tungsten alloy is a tungsten-rhenium alloy.

8. The process of claim 1 wherein the metal utilized in said spraying and depositing steps is tungsten.

9. The process of claim 1 wherein the metal utilized in said depositing step is tungsten which is precipitated by thermally decomposing a mixture comprising hydrogen and a tungsten salt selected from the group consisting of tungsten hexafluoride and tungsten hexachloride.

sisting of tungsten hexafluoride and tungsten hexachloride.

ll. A process as in claim 1 wherein the graphite is sprayed to a thickness of about l mm. and said outer covering layer is deposited to a thickness of about 02 mm.

12. A rotary anode prepared in accordance with the process of claim 11. 

2. The process of claim 1 wherein said spraying step is accomplished by means of a plasma gun.
 3. The process of claim 1 wherein said deposition comprises vapor depositing said metal under vacuum.
 4. The process of claim 1 wherein said deposition comprises precipitating said metal from the gaseous phase.
 5. The process of claim 4 wherein said precipitation is effected by thermal decomposition of metal salt in the presence of hydrogen gas.
 6. The process of claim 1 wherein the tungsten alloy utilized in the spraying and depositing steps is selected from the group consisting of tungsten-rhenium, tungsten-osmium and tungsten-iridium alloys.
 7. The process of claim 6 wherein said tungsten alloy is a tungsten-rhenium alloy.
 8. The process of claim 1 wherein the metal utilized in said spraying and depositing steps is tungsten.
 9. The process of claim 1 wherein the metal utilized in said depositing step is tungsten which is precipitated by thermally decomposing a mixture comprising hydrogen and a tungsten salt selected from the group consisting of tungsten hexafluoride and tungsten hexachloride.
 10. A process for imparting resistance to rotary anodes for X-ray tubes which comprises the steps of: a. Spraying a graphite base at the site of electron impact with tungsten by means of a plasma gun in order to form a uniform coating thereon; and b. subsequently depositing on said coating an outer covering layer of tungsten which is precipitated from the gaseous phase by thermally decomposing a mixture comprising hydrogen and a tungsten salt selected from the group consisting of tungsten hexafluoride and tungsten hexachloride.
 11. A process as in claim 1 wherein the graphite is sprayed to a thickness of about 1 mm. and said outer covering layer is deposited to a thickness of about 0.2 mm.
 12. A rotary anode prepared in accordance with the process of claim
 11. 